Mornin folks, got another totally random issue with my Z to toss out and see what anybody has in the ways of feedback.

Car: 1993 2+2, 151,500 miles, no mods, N/A, automatic.
Issue: Car temp starts to climb at speed over 75 mph.

Trouble shooting done so far:

Codes ran - clean.
Diagnostics at auto shop - clean.

Drove around town out of over drive to keep the RPMs up, in the day heat with the AC on = No overheating.

Sat in traffic with the AC off, no overheating. AC on did make temp climb but no surprise there.

Checked radiator coolent levels, full.
Had radiator flushed and filled.
Checked radiator for blockage, none.

Changed oil and filter, mobile 1 high mileage full synth, 10w 40 and a mobile one filter.

Changed air filters, unsure of brand, got the last 2 in orange county aparently and couldnt be picky.

The shop swears the water pump is fine as is the thermostat.

Car only gets warm at high speeds, low speeds of matching RPM do NOT make the temp climb.

Turning on the heater doe help the temp drop.

If I drop back below 75mph the temp drops on it's own. Example of this, hit 75, temp went up, exited freeway and by the time I hit the end of the off ramp it was back down to normal.


I'm at a total loss here. Nothing makes sense. I'd swear it would be a problem with the water pump or thermostat but I also figure those would happen at low speeds as well.

Ideas??

 

What method did you/they use to flush the system?

An old trick that some people do is drill a tiny hole in the thermostat (around the edge, where the tiny bypass valve is). This will allow more coolant to circulate continually, while also allowing slightly more coolant flow when the thermostat is open.

 

I got it done at Midas this time so they used whatever mechanical pump flush deal they have there. I'm pretty auto-ignorant as far as doing myown repairs and work goes so I'd skip drilling a hole anywhere and just replace the thermostat. They're pretty cheap anyways. 151 thousand miles and I'm pretty sure its the original. Knowing the hard water out here if it's ever been filled with tap water theres a chance something is gummed up with deposits. It wrecks hell on my washer fluid jets at least.

 

Well if you're going to replace the thermostat (which isn't a bad idea), I'd recommend drilling the tiny hole on the new thermostat. It can never hurt to have additional coolant flow (I did it on mine, and many other Z owners I know have done it on theirs, so you can trust me when I say it's safe).

Was the 120k maintenance done?

 

collapsed or collapsing hose. It seems to happen when there is moderate pressure in the system. There is a hose on the rear left hand side of the motor that goes directly from the coolant tube to the drivers side turbo if memory serves. It might be the culprit (or one similar).

 

sounds like what happens every time anyone ever uses a leak stopper for radiators. they clog stuff and make it harder to cool once the thermostat is all the way open.

 

Coincidentally, I was fighting this issue for a while. Everything checked out fine. I ended up spraying out the exterior fins of the radiator and A/C condensor with a high pressure hose. Problem solved. I do live almost two miles up a dirt road so my situation may be a little extreme. It may be worth a try for you. Have you checked to make sure there isn't any trash or debris in front of your radiator?

 

ZLover - Dont belive the 120k maint was done, at least not per the manual. I'll have to double check it. Would you happen to have a pic of the thermostat and where/what size hole to drill?

Goofyz - Not a turbo but still, all hoses checked out fine. Not even a kink or crease.

KasbeKZ - Never used one, never would. However my suspicion of possible hard water deposits seems to go hand in hand with your theory.

CanyonCarver - Yeah, everything is clean and debris free. One of the first things I checked and the mechanic double checked.

 

I don't have a pic, however, it'll be super clear once you are looking at it. On the outer edge of the thermostat, there is this little tiny valve thing that lets coolant constantly circulate through the system (it's a hole with a little flapper-plug device). Drill a hole somewhere around the edge similar to where that is. You're basically adding another bypass without the tiny valve that it has.

And if the 120k maintenance wasn't done, you should *really* consider doing that. Some of your system components are probably worn out and that might make all the difference. Even if the pump doesn't seem to be bad, it might be. (On my old DD, the pump appeared fine, didn't make noise or wobble or anything, but it wasn't circulating coolant well - as a result, it always overheated. I replaced it and the problem went away.) Water pump is part of the kit (as is the thermostat), so I'd really recommend just doing the whole 120k service.

 

Sweet. I'll look into it and see if I can get it done somewhere that won't rape me for parts and labor. Just don't have the knowledge or facilities to do it myself.

Thanks all.

 

don't know if this has been suggested already, but there is a flushing solution that you can get to flush the system. you put powder i think into the coolant and run it for a few minutes then open the system and let it all pump out while you hold a hose or continuous flow of distilled water if you are very picky in the radiator to rinse it very well. then you empty it all back out and fill it up with 50/50. you'd be amazed at all the crap that solution gets out. that would probably get rid of any build ups that may be causing your problem

 

It's something to look into if nothing else fixes it, one thing at a time though. Have to deal with a flat tire first....goddamn Orange County roads...500 miles! 500 fricken miles!!! Thats how long I've had this set of tires and I already picked something up!!!

 

Still have a couple days before I can get the old girl to AltZ in Huntington beach bu tin the mean time I've been pouring over the vast amounts of data linked on this site and found this:

How : The most common symptom of a bad fan clutch is the radiator boiling over a minute or two after the engine has been shut off following general urban driving. If this is happening, you can be 90% sure the fan clutch is bad.

The typical viscous fluid fan clutch works in a manner similar to the torque converter in an automatic transmission. The drive side of the clutch is connected directly to the water pump pulley and turns at the same speed. The side that attaches to the fan is connected to a driven plate. This plate. In operation, the drive side rotates. This induces rotation in the fluid. The rotating fluid then turns the driven plate and this turns the fan.

There is also a bimetalic sensor that operates valving that determines how the viscous fluid contacts the driven plate. The strip is positioned to sense the temperature of the air flowing through the radiator. At low temperatures, the viscous fluid is routed so that little rotational energy is transmitted to the driven plate. Under these conditions, the fan speed will usually be about 40% of the water pump speed. At a predetermined set point, the action of the bimetallic strip directs the flow so that the rotating fluid transfers considerable energy to the driven plate. At this point, the fan blades will turn at about 75-80% of the water pulley speed provided the car is not moving at a significant velocity.


Diagnostic : The fan should rotate about one-half to a full rotation when spun by hand (with the engine off please - no need to lose fingers at this point).

If it spins freely (several rotations), the fan clutch may have failed and the fan will not be able to draw enough air. This is mostly seen if a car overheats at idle vs. when being driven.

Mine does exactly this....except for the whole idel vrs driving thing... Spun the fan last night by hand and wondered "Hmmm...shouldnt it NOT be spinning this easy???"

Ah hell, we'll see. Damn shame its hotter than it has been all year right now....stupid California weather..

 

if your fan clutch is bad you might be able to do a temporary fix and pull out the pin that is behind the metal strap that runs across the front of your fan clutch and make it fully engaged all the time it will drop preformance but will cool your engine.

i had to do this on my 300sd benz.

also change the clutch when you have time and money as this shouldnt be a permanent fix since it will hinder preformance and over cool in the winter

 

The fan-clutch should have little effect during high speed driving. Have you checked your base ignition timing? If it's advanced, you temps can go up.

 

Turns out the fan is working normally as well...ignition hasnt been checked but that'll be something for Tony tomorrow.

I'm totally at a loss right now, absolutely clueless as to what this could be and praying it's cheap and easy to fix. Basically it's all hopes and dreams and adding water every time the engine cools down until I get it into the shop tomorrow.

 

Alrighty, well my car is back from the shop and running like a champ now. What was wrong? Who knows...there were so many little things that were either going wrong, could go wrong or were just not worth the effort of tearing the engine apart to get at again if we didnt fix it the first time we just decided to gut the majority of the cooling system and hope for the best.

All told I had the shop replace:

Radiator
Radiator cap
Upper and lower radiator hoses
Thermostat
Inlet pipe
Fan clutch
Fan
Fan belt
Compressor belt
Power steering belt

Total on parts: 827.92
Total on labor: 368.00
Total with tax: 1260.08

More than I wanted to spend but WAY less than I feared. Tony does great work too, all parts are factory new and he guentees his work forever unless you drive like some tweeker rice boy in a civic.

Alt Z inc. for all you Z lovers in and around the Huntington Beach area.

Me is a happy guy, ahh closure.

 

That was alot of money. You should have has a t-belt and waterpump thrown in for good measure.

 

well glad it's fixed. the very first thing I would have checked would be the head gaskets but I'm VERY glad that wasn't your problem.

nobody mentioned head gaskets in here.. are the VG30DE engines not prone to blowning those because they're built for high compression?

 

they do blow, but it wasn't suggested because there would have been other very obvious symptoms, like milky oil, or oil in the antifreeze.

 

One of the best ways I've found to check that is a gasoline oder to your overflow water, there wasnt any so I never mentioned it. But Tony confirmed my HG was just fine.

Timing belt was replaced along with everything else and my water pump was just fine so no need to replace it. I actually think it was replaced less than 2 years ago.

All in all I'm just glad my car is back and running right. Was driving my girls Dodge Ram...felt like I was riding in a battle ship.

 

I remeber when i first got my 1993 300zx 2+2 i took it out on the free way and low nad behold it wouldnt shift into 3rd gear after 65 mph the engine quickly heated up i pulled over to inspeck it ... found out the tranny fliud was never changed so i slowly got the car home pulled off the tranny pan and went down to autozone to get a new tranny filter and synthetic tranny oil... wow it helped out alot ! no more heating up for me... 145mph and still no overheating for me ! I LOVE THE TEXAS HIGH WAY TO LUBBOCK ! lol ;-)

 

I CERTAINLY CERTAINLY CERTAINLY FOR YOUR SAKE hope they replaced the coolant bypass hoses while they were in their doing the thermostat...

http://www.conceptzperformance.com/C...5207.119.72.39


They are 5 bucks, I replace mine every time i take the hard water pipes off, which isn't that often really, but still....

 

Yep, covered that too.

When I say these guys gutted and replaced my cooling system, I mean they took out EVERYTHING and replaced with brand new Nissan certified parts, every single thing that has water flowing through it minus the engine block itself...well, and the water pump because that was basically new anyways.

Tony does some very good work, he's also got a neat little 280Z road racer with an old Ferraribody on it I should get some pics of his shop and post em, kinda fun to look at.

 

I've seen one of those. they look like the old ferrari bugato's or w/e there called and however their spelled. They look pretty cool.